2025 ISAKOS Biennial Congress ePoster
Measuring Osteotomy Wedge Angle Is More Important Than Measuring Wedge Height In Open Wedge Osteotomies Around The Knee
Julius Watrinet, MD, Dr. med. GERMANY
Johannes Schlaich, Stud., Marburg GERMANY
Romed Peter Vieider, MD, Munich GERMANY
Marco-Christopher Rupp, MD, Munich, Bavaria GERMANY
Julian Mehl, MD, Munich, Bavaria GERMANY
Sebastian Siebenlist, MD, MHBA, Prof., Munich, Bavaria GERMANY
Armin Runer, PD MD, Munich GERMANY
TUM University Hospital, Department of Sports Orthopaedics, Munich, GERMANY
FDA Status Not Applicable
Summary
In Osteotomy planning, the hinge angle is the most reliable parameter while wedge height can be altered by naturally occurring variations in osteotomy entry and hinge point influencing the accuracy of postoperative correction.
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Abstract
Purpose
In preoperative osteotomy planning for medial open wedge high tibial osteotomies (HTO) or lateral open wedge distal femur osteotomies (DFO), wedge height measurement is considered a primary parameter in achieving accurate correction, however it remains unclear whether the accuracy of this parameter is affected by intraoperative variance of osteotomy entry point and length. The purpose of this study was to investigate the impact of the selection of osteotomy entry and hinge point on typical preoperative planning parameters such as wedge height, wedge angle, and osteotomy depth in HTO and DFO and to determine, which of these parameters is most robust.
It was hypothesized that there was a direct correlation between wedge angle, wedge height and osteotomy depth, resulting in a lower variability of the wedge angle compared to the wedge height.
Methods
This retrospective case series analysed whole leg radiographs of 40 patients who underwent HTO or DFO between September 2018 and March 2024. Osteotomy planning was performed using a two-dimensional digital planning software, generating 27 osteotomy variants for each HTO patient (correcting the weight-bearing axis (WBA) to 50% tibial width(TW)) and 21 osteotomy variants for each DFO patient (correcting WBA to 55% TW) by combining different entry and hinge points points resulting in a total of 960 variants. Osteotomy depth, wedge height, and wedge angles were measured for each variant. Bivariate correlations and multiple linear regressions were utilized to assess the relationships between these variables. Finally, a mathematical formula was developed to predict the wedge height based on the wedge angle and the osteotomy depth, which was compared with the actual parameters from the preoperative planning.
Results
The wedge angle in different osteotomy variants per patient remained approximately constant in each preoperative planning with a mean deviation 0.06° ± 0.07°, while the wedge height differed by 0.7mm ± 0.5mm (range?) depending on osteotomy entry point and osteotomy length. Significant positive correlations were observed between wedge height and both opening angle (R = 0.83, p < 0.001) and osteotomy depth (R = 0.60, p < 0.001). Multiple linear regression identified opening angle (Estimate = 0.9, p < 0.001) and osteotomy depth (Estimate = 0.1, p < 0.001) as significant independent predictors of wedge height. A strong correlation was found between actual wedge height and the formula-derived prediction for wedge height (R = 0.998, p < 0.001), with minimal deviation (mean deviation = -0.01° ± 0.1°).
Conclusion
This study demonstrates that osteotomy planning for HTO and DFO should not rely on wedge height only, as naturally occurring variations in osteotomy entry and hinge point influence the accuracy of postoperative correction. Among the planning parameters, the hinge angle is the most reliable parameter. If entry or hinge point do not match preoperatively planning, correct limb alignment should be verified not only by wedge height.